As is known in the art, a variety of computing devices are often connected together to form a computer network. The computer network may be a Local Area Network ("LAN") that connects devices over a small geographical area, or a Wide Area Network ("WAN") that connects devices over a large geographical area. The computing devices include video cameras, CD-ROMs, microphones, televisions, computers, modems, cable modems and other devices that send high resolution images, graphical images, moving images, audio and data in addition to textual information. Different types of computer networks may be interconnected to each other to form larger computer networks (e.g., the Internet). The interconnections include LAN-LAN, LAN-WAN, WAN-WAN, LAN-WAN-LAN, and other network interconnections.
The computing devices transfer multimedia information (e.g., audio, video and data) between two or more computer networks. Transferring multimedia information between two computer networks may or may not require a reserved bit rate transmission capacity, and a reserved bandwidth possibly for the total duration of the transaction. For example, multimedia information for a ten second video clip with sound that is being sent between two points in a Ethernet LAN, requires a significant portion of a 10 Mega-bits-per-second ("Mbps") data transmission capacity available on the LAN for ten seconds to send the multimedia information.
Gateways connect computer networks using different network protocols operating at different transmission capacities. For example, a gateway may have network connections to serial data lines connected to one or more modems. The serial data lines may be used one at a time at a relatively low transmission speed (e.g., 14,400 bps, 28,800 bps, or 56,000 bps) or can be bundled into a group at a higher transmission speed. In contrast, the gateway may also have one or more LAN connections (e.g., Ethernet, Token Ring, or Fiber Distributed Data Interface ("FDDI")). The LAN connections are higher speed connections (e.g., 10 Mbps) and are shared among multiple devices.
The gateway translates information contained in a first protocol being used on a first network connection into a second protocol being used on second network connection, and visa-versa, without undue delay or loss of information. For example, a modem operating at 28,800 bps may be using the International Telecommunications Union-Telecommunication Standardization Sector ("ITU-T", formerly known as the CCITT) H.324 audio/video conferencing protocol and a LAN operating at 10 Mbps may be using the ITU-T H.323 audio/video conferencing protocol for a video conferencing connection. A gateway translates H.323 from the LAN into H.324 for use on the modem, and visa-versa, without undue delay or loss of information even though the LAN is transmitting information at 10 Mbps and the modem is transmitting information at 28,800 bps.
However, the gateway may also translate H.323 on a LAN to H.323 on a serial line using the Point-to-Point Protocol ("PPP"), H.323 on a LAN to H.320 on an Integrated Services Digital Network ("ISDN") line, or translate H.32x on a LAN or a serial line to H.32x on a LAN or a serial line. The gateway is also responsible for maintaining timing relationships and packet sequencing even though a first protocol may use timing relationships and a second protocol may not use timing relationships.
When gateways are used to translate multimedia information between two computer networks, logical multimedia channels are typically created with separate audio, video and data channels. The audio and video channels are typically allocated with predetermined, fixed maximum bandwidth. For example, on a modem connection a audio channel may have a bandwidth of 5,300 bps and a video channel may have a bandwidth of 23,500 bps for a multimedia bandwidth of 28,800 bps. A LAN connection may use audio and video channels with larger bandwidth allocations since the LAN is capable of transmitting information at a much larger overall multimedia bandwidth (e.g., 10 Mbps).
There are several problems associated with using gateways or other internetworking devices known in the art to interconnect computer networks operating at different transmission capacities. For example, the logical channels for larger bandwidth computer network connections (e.g., LAN connections) are often connected to logical channels for smaller bandwidth computer network connections (e.g., modem connections). The larger bandwidth connections have no way of determining they are connected to smaller bandwidth, and more constrained connections. This will cause a constant congestion problem on a gateway since the logical channels for the larger bandwidth network is constantly transmitting more information than can be accepted by the lower bandwidth network. In addition, the gateway must translate between two or more different protocols for the connections without undue delay or loss of information.
If data is sent along with the audio and video information on a multimedia connection, the congestion problems are further aggravated on the gateway. The gateway allocates a chunk of transmission bandwidth for a logical data channel. Since the data transmission is typically very bursty, the transmission bandwidth allocated for data channel is often wasted when no data is being sent. For example, the gateway may allocate a 5,000 bps logical data channel for each network connection using the data. For a modem with a bandwidth of 28,800 bps, this wastes about 17% of the available bandwidth on the modem. This is a significant waste of bandwidth on a smaller bandwidth network connection.
Another problem is that the gateway must maintain timing relationships and packet sequencing translating between certain protocols. The timing relationships and packet sequencing must be maintained even though a first protocol uses timing and a second protocol does not.